The present invention relates to a semiconductor device with a capacitor using tungsten nitride as a material to form an electrode, and a method of manufacturing the same.
In a dynamic random access memory (DRAM) comprised of one transistor and one capacitor, along with an increase in integration degree of the integrated circuit, it is required to increase the memory capacity by reducing the memory cell area. In this requirement, a technique has been proposed which increases the substantial area by forming a capacitor with a cylindrical or multilayered electrode structure, so that the memory capacity is increased without increasing the memory cell size.
For example, when a cylindrical capacitor structure is to be employed, a plate electrode which forms a capacitor is formed on a capacitor film having a large step. A conductor layer serving as the plate electrode to be formed on the capacitor film must be formed continuously including a step portion produced by the thickness portion of the capacitor film. Tungsten nitride, titanium nitride, ruthenium, or the like that can be formed with a good step coverage is used as the material of the conductor film, because these conductive materials can form a film by chemical vapor deposition (CVD) having a good step coverage. Among these conductive materials, tungsten nitride is superior in terms of adhesion properties and easiness to be processed to the electrode, and low leakage. Tungsten nitride is less expensive and easier to be processed to the electrode than ruthenium. Also, tungsten nitride can form a film with less damaging to an underlying capacitor film than titanium nitride.
A DRAM using above tungsten nitride will be described.
As shown in FIG. 3, a gate electrode 704 is formed on that region on a semiconductor substrate 701, which is defined by an isolation region 702 through a gate insulating film 703. Impurity regions are formed in the semiconductor substrate 701 on the two sides of the gate electrode 704 by ion implantation or the like using the gate electride 704 as a mask, thereby forming source/drain regions 705.
An interlevel insulating film 706 is formed on the gate electrode 704 over the entire surface of the semiconductor substrate 701. A contact plug 707 to be connected to the corresponding source/drain region 705 formed in the semiconductor substrate 701 is formed at a predetermined position of the interlevel insulating film 706. A bit line 708 is formed to be connected to the contact plug 707.
An interlevel insulating film 709 is formed on the interlevel insulating film 706 including the bit line 708. A contact plug 710 to be connected to the corresponding source/drain region 705 formed in the semiconductor substrate 701 is formed to extend through the interlevel insulating films 709 and 706. A storage electrode 711 is formed on the contact plug 710 through a barrier film 710a. 
A capacitor insulating film 712 is formed to cover the storage electrode 711, and a plate electrode 713 made of tungsten nitride is formed to cover the storage electrode 711 and capacitor insulating film 712.
In this manner, a transistor comprised of the gate electrode 704, and a capacitor to be connected to this transistor and comprised of the storage electrode 711, capacitor insulating film 712, and plate electrode 713 make up the basic unit of the memory cell.
An interlevel insulating film 714 made of an insulator is formed also on the interlevel insulating film 709 including the plate electrode 713. Although not shown, an interconnection layer to be connected to the bit line 708 and plate electrode 713 (described above) is formed on the interlevel insulating film 714.
In the above semiconductor device, after the interlevel insulating film is formed on the plate electrode, for example, when a contact between the interconnection formed on the interlevel insulating film on the plate electrode and the silicon substrate is to be formed, high-temperature annealing at approximately 600xc2x0 C. is sometimes performed. If such a high temperature is applied, cracking may occur in the plate electrode or in the worst case, the plate electrode may be peeled.
It is, therefore, the principal object of the present invention to provide a method of manufacturing a semiconductor device, by which even if a high temperature is applied in the post-process to a tungsten nitride electrode which forms a capacitor, cracking or peeling will not occur in the electrode.
In order to achieve the above object, according to the present invention, there is provided a semiconductor device comprising at least one interlevel insulating film arranged on a semiconductor substrate, a first electrode made of a metal material and arranged on the interlevel insulating film, a capacitor insulating film made of an insulating metal oxide and arranged on the first electrode, a second electrode made of tungsten nitride and arranged on the capacitor insulating film, and a protective film arranged on the second electrode to suppress outward diffusion of nitrogen from the second electrode.